This invention relates generally to fuel nozzles, and more specifically fuel nozzle assemblies having unitary components coupled using brazing for use in gas turbine engines.
Turbine engines typically include a plurality of fuel nozzles for supplying fuel to the combustor in the engine. The fuel is introduced at the front end of a burner in a highly atomized spray from a fuel nozzle. Compressed air flows around the fuel nozzle and mixes with the fuel to form a fuel-air mixture, which is ignited by the burner. Because of limited fuel pressure availability and a wide range of required fuel flow, many fuel injectors include pilot and main nozzles, with only the pilot nozzles being used during start-up, and both nozzles being used during higher power operation. The flow to the main nozzles is reduced or stopped during start-up and lower power operation. Such injectors can be more efficient and cleaner-burning than single nozzle fuel injectors, as the fuel flow can be more accurately controlled and the fuel spray more accurately directed for the particular combustor requirement. The pilot and main nozzles can be contained within the same nozzle assembly or can be supported in separate nozzle assemblies. These dual nozzle fuel injectors can also be constructed to allow further control of the fuel for dual combustors, providing even greater fuel efficiency and reduction of harmful emissions. The temperature of the ignited fuel-air mixture can reach an excess of 3500° F. (1920° C.). It is therefore important that the fuel supply conduits, flow passages and distribution systems are substantially leak free and are protected from the flames and heat.
Over time, continued exposure to high temperatures during turbine engine operations may induce thermal gradients and stresses in the conduits and fuel nozzle components which may damage the conduits or fuel nozzle components and may adversely affect the operation of the fuel nozzle. For example, thermal gradients may cause fuel flow reductions in the conduits and may lead to excessive fuel maldistribution within the turbine engine. Exposure of fuel flowing through the conduits and orifices in a fuel nozzle to high temperatures may lead to coking of the fuel and lead to blockages and non-uniform flow. To provide low emissions, modern fuel nozzles require numerous, complicated internal air and fuel circuits to create multiple, separate flame zones. Fuel circuits may require heat shields from the internal air to prevent coking, and certain fuel nozzle components may have to be cooled and shielded from combustion gases. Additional features may have to be provided in the fuel nozzle components to promote heat transfer and cooling. Furthermore, over time, continued operation with damaged fuel nozzles may result in decreased turbine efficiency, turbine component distress, and/or reduced engine exhaust gas temperature margin.
Improving the life cycle of fuel nozzles installed within the turbine engine may extend the longevity of the turbine engine. Known fuel nozzles include a delivery system, a mixing system, and a support system. The delivery system comprising conduits for transporting fluids delivers fuel to the turbine engine and is supported, and is shielded within the turbine engine, by the support system. More specifically, known support systems surround the delivery system, and as such are subjected to higher temperatures and have higher operating temperatures than delivery systems which are cooled by fluid flowing through the fuel nozzle. It may be possible to reduce the thermal stresses in the conduits and fuel nozzles by configuring their external and internal contours and thicknesses. Some known conventional fuel nozzles have 22 braze joints and 3 weld joints.
Fuel nozzles have swirler assemblies that swirl the air passing through them to promote mixing of air with fuel prior to combustion. The swirler assemblies used in the combustors may be complex structures having axial, radial or conical swirlers or a combination of them. In the past, conventional manufacturing methods have been used to fabricate mixers having separate venturi and swirler components that are assembled or joined together using known methods to form assemblies. For example, in some mixers with complex vanes, individual vanes are first machined and then brazed into an assembly. Investment casting methods have been used in the past in producing some combustor swirlers. Other swirlers and venturis have been machined from raw stock. Electro-discharge machining (EDM) has been used as a means of machining the vanes in conventional fuel nozzle components.
Conventional gas turbine engine components such as, for example, fuel nozzles and their associated swirlers, conduits, distribution systems, venturis and mixing systems are generally expensive to fabricate and/or repair because the conventional fuel nozzle designs having complex swirlers, conduits and distribution circuits and venturis for transporting, distributing and mixing fuel with air include a complex assembly and joining of more than thirty components. More specifically, the use of braze joints can increase the time needed to fabricate such components and can also complicate the fabrication process for any of several reasons, including: the need for an adequate region to allow for braze alloy placement; the need for minimizing unwanted braze alloy flow; the need for an acceptable inspection technique to verify braze quality; and, the necessity of having several braze alloys available in order to prevent the re-melting of previous braze joints. Moreover, numerous braze joints may result in several braze runs, which may weaken the parent material of the component. Modern fuel nozzles such as the Twin Annular Pre Swirl (TAPS) nozzles have numerous components and braze joints in a tight envelope. The presence of numerous braze joints can undesirably increase the weight and the cost of manufacturing and inspection of the components and assemblies.
Accordingly, it would be desirable to have a fuel nozzle having unitary components having complex geometries for mixing fuel and air in fuel nozzles while protecting the structures from heat for reducing undesirable effects from thermal exposure described earlier. It is desirable to have a fuel nozzle assembly having assembly features to reduce the cost and for ease of assembly as well as providing protection from adverse thermal environment and for reducing potential leakage. It is desirable to have a method of assembly of unitary components having complex three-dimensional geometries, such as, for example, a distributor, a swirler and a venturi with a heat shield for use in fuel nozzles having reduced potential for leakage in a gas turbine engine. It is desirable to have a method of manufacturing unitary components having complex three -dimensional geometries for use in fuel nozzles.